QuestionAugust 27, 2025

U= xvert xis a positive integer greater than1 Which is an empty set? xvert xin Uand(1)/(2)xis prime xvert xin Uand2xis prime xvert xin Uand(1)/(2)xcanbewrittenasafraction xvert xin Uand2xcanbewrittenasafraction

U= xvert xis a positive integer greater than1 Which is an empty set? xvert xin Uand(1)/(2)xis prime xvert xin Uand2xis prime xvert xin Uand(1)/(2)xcanbewrittenasafraction xvert xin Uand2xcanbewrittenasafraction
U= xvert xis a positive integer greater than1 
Which is an empty set?
 xvert xin Uand(1)/(2)xis prime 
 xvert xin Uand2xis prime 
 xvert xin Uand(1)/(2)xcanbewrittenasafraction 
 xvert xin Uand2xcanbewrittenasafraction

Solution
4.3(128 votes)

Answer

\{ x \mid x \in U \text{ and } 2x \text{ is prime} \} is an empty set. Explanation 1. Analyze the first set condition For \{ x \mid x \in U \text{ and } \frac{1}{2}x \text{ is prime} \}, since x is a positive integer greater than 1, \frac{1}{2}x cannot be an integer unless x is even. If x = 2k, then \frac{1}{2}x = k. For k to be prime, k must be an integer greater than 1. This set is not empty. 2. Analyze the second set condition For \{ x \mid x \in U \text{ and } 2x \text{ is prime} \}, if 2x is prime, then 2x must be equal to 2 (the only even prime number). This implies x = 1, which contradicts x > 1. Thus, this set is empty. 3. Analyze the third set condition For \{ x \mid x \in U \text{ and } \frac{1}{2}x \text{ can be written as a fraction} \}, any real number can be expressed as a fraction. Therefore, this set is not empty. 4. Analyze the fourth set condition For \{ x \mid x \in U \text{ and } 2x \text{ can be written as a fraction} \}, any real number can be expressed as a fraction. Therefore, this set is not empty.

Explanation

1. Analyze the first set condition<br /> For $\{ x \mid x \in U \text{ and } \frac{1}{2}x \text{ is prime} \}$, since $x$ is a positive integer greater than 1, $\frac{1}{2}x$ cannot be an integer unless $x$ is even. If $x = 2k$, then $\frac{1}{2}x = k$. For $k$ to be prime, $k$ must be an integer greater than 1. This set is not empty.<br /><br />2. Analyze the second set condition<br /> For $\{ x \mid x \in U \text{ and } 2x \text{ is prime} \}$, if $2x$ is prime, then $2x$ must be equal to 2 (the only even prime number). This implies $x = 1$, which contradicts $x > 1$. Thus, this set is empty.<br /><br />3. Analyze the third set condition<br /> For $\{ x \mid x \in U \text{ and } \frac{1}{2}x \text{ can be written as a fraction} \}$, any real number can be expressed as a fraction. Therefore, this set is not empty.<br /><br />4. Analyze the fourth set condition<br /> For $\{ x \mid x \in U \text{ and } 2x \text{ can be written as a fraction} \}$, any real number can be expressed as a fraction. Therefore, this set is not empty.
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